单项选择题
Which of the listed types steam traps operates on the principle that hot water flashes to steam when its vapor pressure is rapidly reduced?（）
A.Ball float B.Thermostatic C.Bimetallic D.Impulse
单项选择题 On all vessels equipped with refrigeration units of over 20 cubic foot capacity, （）.
单项选择题 The emergency bilge suction valve is typically used （）.
单项选择题 Short cycling of a refrigeration compressor refers to （）.
